Modified preceramic polymers, method of making and ceramic matrix composite formed therefrom

ABSTRACT

Disclosed is a modified preceramic polymer having a polymer backbone consisting of silicon or a combination of silicon and carbon; and a pendant modifier bonded to the backbone wherein the modifier includes silicon, boron, aluminum, a transition metal, a refractory metal, or a combination thereof. The modified preceramic polymer can be used to form a ceramic matrix composite.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 16/692,620filed Nov. 22, 20219, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND

Exemplary embodiments pertain to the art of preceramic polymers, methodsof making preceramic polymers and ceramic matrix composites made frompreceramic polymers.

Silicon carbide (SiC) and other ceramic materials are used to producearticles having high structural and mechanical strength at a temperatureabove 1,200° C. (2,200° F.). The articles are can be used in aerospaceand other industries needing resistance to heat. As operationtemperatures increase above 1,200° C., material options for the articlesdecrease because metal and metal alloys are not viable. While ceramicmatrix composites (CMCs) and carbon-carbon (C/C) materials areconventionally used at these temperatures, these materials are expensiveand time intensive to produce by conventional precursor impregnation andpyrolysis, slurry infiltration, melt infiltration, or chemical vaporinfiltration techniques. Processing of the CMCs and C/C materialsrequires multiple heat treatments and processing steps to densify thematerials and provide the desired densities and strengths. ProducingCMCs typically requires multiple infiltration cycles, which increasesthe overall cost and amount of time to fabricate the CMCs. Additionally,conventional furnaces used to produce the articles are limited in theirability to uniformly process larger articles, such as those needed forlarge rocket and turbine engine components, structural housings,combustors, and similar articles.

One method of forming SiC and other ceramic materials is from preceramicpolymers. One commonly used preceramic polymer is polycarbosilane.However, the ceramic materials formed from conventional polycarbosilanecannot be used at the increasing temperatures needed for newapplications. Improved preceramic polymers are desired.

BRIEF DESCRIPTION

Disclosed is a modified preceramic polymer having a polymer backboneconsisting of silicon or a combination of silicon and carbon; and apendant modifier bonded to the backbone wherein the pendant modifierincludes silicon, boron, aluminum, a transition metal, a refractorymetal, or a combination thereof.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the pendant modifierincludes silicon, boron, aluminum, or a combination thereof.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the pendant modifierincludes titanium, zirconium, hafnium, vanadium, chromium, or acombination thereof.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the pendant modifierincludes niobium, tantalum, molybdenum, tungsten, rhenium, or acombination thereof.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the pendant modifier tobackbone silicon atomic ratio is 4:1 to 0.05:1.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the pendant modifier tocarbon atomic ratio is 4:1 to 0.05:1.

Also disclosed is a method of making a modified preceramic polymerincluding reacting a preceramic polymer with a modifier source selectedfrom the group consisting of silicon compounds having a reactive group,boron compounds having a reactive group, organometallic compounds havinga reactive group, metal organic compounds having a reactive group,functionalized inorganic particulates having a reactive group, andcombinations thereof. The preceramic polymer has a polymer backboneconsisting of silicon or a combination of silicon and carbon.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the organometalliccompound includes a metal amine.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the reactive groupincludes amines, tri-functional silanes, halides, hydrides, amides,hydroxides, silyl groups, vinyl groups, allyl groups, alkoxides,alcohols, substituted ethers, and combinations thereof.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the preceramic polymeris a mixture of polysilane and polycarbosilane.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the preceramic polymerincludes a vinyl group.

Also disclosed is a ceramic matrix composite comprising reinforcingfibers and a matrix, wherein the matrix comprises silicon carbide andmetal carbide and the metal carbide is homogeneously dispersedthroughout the silicon carbide.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the ceramic matrixcomposite further includes a metal boride.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the metal carbides aredispersed on a sub-nanometer level.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the metal carbides aredispersed on a molecular level.

Also disclosed is a method of making a ceramic matrix compositecomprising infiltrating a fiber preform with a modified preceramicpolymer to form an infiltrated preform and pyrolyzing the infiltratedpreform to form the ceramic matrix composite, wherein the modifiedpreceramic polymer has a polymer backbone consisting of silicon or acombination of silicon and carbon; and a pendant modifier bonded to thepolymer backbone. The pendant modifier includes silicon, boron,aluminum, a transition metal, a refractory metal, or a combinationthereof.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation.

A modified preceramic polymer useful for forming a composite materialhaving a low mass loss and a high ceramic yield is disclosed, as aremethods of forming the modified preceramic polymer and the compositematerial. The modified preceramic polymer includes pendant modifiersbonded to the preceramic polymer backbone. Preceramic polymers formceramics by pyrolyzing to form ceramic compounds such as silicon carbidefrom the silicon and carbon present in the preceramic polymer. Thependant modifiers increase the char yield (the ceramic yield) afterpyrolysis by forming carbides, for example, with excess carbon atomsthat do not form silicon carbide with the silicon from the polymerbackbone.

The modified preceramic polymer is produced by reacting the preceramicpolymer with a modifier source. The preceramic polymer comprises apolymer backbone. The polymer backbone consists of silicon or acombination of silicon and carbon. When the polymer backbone consists ofsilicon the preceramic polymer is a polysilane. When the polymerbackbone consists of silicon and carbon the preceramic polymer is apolycarbosilane.

Polysilanes are formed of repeating units having formula (I)

and polycarbosilanes are formed of repeating units having formula (II)

where R¹ and R² of each repeating unit is independently a hydrogen (H)group, a methyl (CH₃) group, a vinyl group (CH═CH₂), or an allyl group(CH₂—CH═CH₂) and n is an integer from 2 to 10,000 (e.g., from 100 to5,000). In polycarbosilanes formed of repeating units having formula(II) the polymer backbone consists of silicon and carbon in methylenegroups. In the repeating units having formula (I) and (II) R¹ and R² arenot part of the polymer backbone. When vinyl groups are present, thevinyl group may be directly bonded to the silicon atom or may be bondedto the silicon atom by an alkyl group or other linker. By way of exampleonly, the alkyl group may include from one carbon atom to six carbonatoms. In some embodiments at least a portion of the repeating units inthe polycarbosilane or polysilane include the vinyl group as R¹ or R².The preceramic polymer may include at least about 0.01 vinyl eq/kg, suchas 0.2 vinyl eq/kg to about 5.0 vinyl eq/kg. The preceramic polymer mayalso include at least about 0.01 hydride eq/kg, such as from about 0.2hydride eq/kg to about 10 hydride eq/kg.

Polysilanes and polycarbosilanes are commercially available fromnumerous sources including, but not limited to, EEMS, LLC (SaratogaSprings, N.Y.), Starfire Systems, Inc. (Schenectady, N.Y.), or Matech(Westlake Village, Calif.), Gelest, Nippon Soda Co, Union Carbide andMomentive. The polycarbosilane may include, but is not limited to,SMP-10, StarPCS® SMP-500, or StarPCS® SMP-877 silicon carbide precursorfrom Starfire Systems, Inc. (Malta, N.Y.). Additional polycarbosilanesare commercially available from EEMS, LLC as MS 208, MS 272, MS 250, MS440, CSO 110, or CSO 116. The polysilane may also include a combinationof polysilanes and the polycarbosilane may also include a combination ofpolycarbosilanes. Commercially available polysilanes may include acombination of polysilanes and commercially available polycarbosilanesmay include a combination of the polycarbosilanes.

Exemplary modifier sources include inorganic particulates functionalizedwith a reactive group, organometallic compounds having a reactive group,metal organic compounds having a reactive group, silicon compoundshaving a reactive group, and boron compounds having a reactive group.

Exemplary reactive groups include amines, tri-functional silanes,halides, hydrides, amides, hydroxides, silyl groups, vinyl groups, allylgroups, alkoxides, alcohols, substituted ethers, and combinationsthereof.

Exemplary inorganic particulates include metal powders, ceramic powders,and carbon coated metal powders or carbon coated ceramic powders. Theinorganic particulates may have an average diameter of 200 nanometers to100 micrometers. The inorganic particulates can be functionalized with areactive group by solution or vapor based coating methods, plasma spray,fluidized bed processing, and the like.

Exemplary organometallic compounds having a reactive group include thosecompounds having ligands which form volatile leaving groups such asamines, tri-functional silanes, halides, amides, hydroxides, alkoxides,alcohols, substituted ethers, and combinations thereof. Exemplary metalsinclude aluminum, transition metals and refractory metals. Exemplarytransition metals include titanium, zirconium, hafnium, vanadium,chromium, or a combination thereof. Exemplary refractory metals includeniobium, tantalum, molybdenum, tungsten, rhenium, or a combinationthereof. Organometallic compounds may include alkyl and aryl substitutedmetals, metal amines and metal carbonyls.

Exemplary silicon compounds having a reactive group include allyltrialkoxy silanes, triallyl methyl silane, organosilanes, disilanes,trisilane, and other non-carbon containing silanes. Exemplary boroncompounds having a reactive group include organoboranes and trialkylboranes.

Metal organic compounds may include tantalum pentakis (dimethyl amide),hafnium diethylamide, hafnium tetrakis (ethylmethyl amide), andzirconium tetrakis (dimethylamide).

The preceramic polymer and modifier source are reacted to form themodified preceramic polymer which has a backbone consisting of siliconor a combination of silicon and carbon. The pendant modifier includesmetal atoms bonded to the silicon, a pendant carbon or to both.Exemplary structures of the repeating units having a modifier are shownbelow

R^(s), R^(w), and R^(x) are individually a pendant modifier as describedabove. R^(s), R^(w) and R^(x) may all be present, may be presentindividually, or may be present in some combination. R^(s), R^(w) andR^(x) are functional groups derived from the modifier source. Themodified preceramic polymer may include repeating units havingfunctional groups derived from the modifier source as well as repeatingunits shown in formulas (I) and/or (II).

Reaction conditions may include the use of neat materials, the use ofsuitable solvents for one or both of the reactants, mild stirring oragitation, ultrasonic or microwave exposure, heating to temperatures ashigh as 150° C., controlled atmospheres such as inert gas (e.g. argon,helium), reactive atmospheres (e.g. ammonia, hydrogen), reducingatmospheres (e.g. ammonia, hydrogen, carbon monoxide), or sufficientvacuum to remove residual solvent and/or volatile by-products.Additional free radical inducing agents can be introduced to facilitatereaction at the vinyl group.

The modified preceramic polymer may have a pendant modifier to backbonesilicon atomic ratio of 4:1 to 0.05:1.

The modified preceramic polymer may have a pendant modifier to carbonatomic ratio of 4:1 to 0.05 to 1.

The modified preceramic polymer may be used to infiltrate a preform madeof fibers. Exemplary fibers include carbon fibers, metal fibers, ceramicfibers (e.g. SiC, Si₃N₄, SiOC, Al₂O₃), glass fibers, E-glass, S2 glass,aramid fibers, e.g., KEVLAR®, polyethylene fibers, e.g., SPECTRA®,coated carbon fibers (e.g., BN coated carbon fibers, BN/SiC coatedcarbon fibers), carbon fibers with a surface converted to SiC, coatedSiC fibers, or combinations thereof. Fibers can be continuous, chopped,woven, braided, discontinuous, uniaxially arranged, or otherwiseconfigured as known in the art.

It is further contemplated that a preceramic polymer may be used toinfiltrate a preform prior to modification. The preceramic polymer inthe preform may then be reacted with a modifier source to form amodified preceramic polymer. The reaction to form the modifiedpreceramic polymer may be carried out by atomic layer deposition (ALD),molecular layer deposition (MLD), sequential vapor infiltration (SVI),or a combination thereof.

Following infiltration the infiltrated preform including a modifiedpreceramic polymer is subjected to pyrolysis or thermal conversion undercontrolled atmosphere(s), temperature(s) and time(s) to form a ceramicmatrix comprising silicon carbide and additional metal carbide.Exemplary temperatures are 900° C. to 2000° C. Exemplary times are 0.5hr to 100 hr. Exemplary atmospheres include inert gas (e.g. argon,helium), reactive (e.g. nitrogen) or reducing atmospheres (CO,hydrogen), low pressure or vacuum, or combinations thereof. When boronis present in the modified preceramic polymer, the ceramic matrix mayfurther include metal borides.

In some embodiments the modified preceramic polymer is cured prior topyrolysis or thermal conversion. Curing includes exposure to externalradiation, such as heating, at temperatures up to 250° C. at exposuretimes ranging from minutes to hours. Alternate external radiation suchas microwave and intense pulsed light from xenon flash lamps is alsocontemplated. The metals in the cured modified preceramic polymer may besupplemented with additional inorganic atoms which may be chemically thesame or different from the existing inorganic atoms.

The additional inorganic atoms may be incorporated into the curedmodified preceramic polymer by atomic layer deposition (ALD), molecularlayer deposition (MLD), sequential vapor infiltration (SVI) or acombination thereof “Incorporated” includes chemical bonding and/orinfiltration into the volume of the cured modified preceramic polymer.Chemical bonding includes all types of chemical bonding, for example,covalent and ionic. The term “sequential vapor infiltration” includesvariants such as multiple pulse infiltration and sequential infiltrationsynthesis. Sequential vapor infiltration diffuses reactants into thepolycarbosilane (neat or modified) and incorporates the inorganicspecies below the surface of the material. Incorporated inorganicspecies result in bonded inorganic atoms following conversion steps toform the ceramic matrix. SVI, ALD and/or MLD may be combined to resultin the desired distribution of inorganic species.

The composite materials and CMCs according to embodiments of thedisclosure have a greater than 10% improvement in ceramic yield relativeto the ceramic yield of the corresponding unmodified preceramic polymer.Since relatively less mass is lost during thermal processing, thecomposite materials and CMCs containing the modified preceramic polymerretain their shape and structural functionality without using theextensive fabrication typically required to produce conventional CMCs.The relatively low mass loss corresponds to lower porosity of thecomposite materials and CMCs, eliminating the need for additionalinfiltration cycles, which are performed in conventional CMCs and aretime consuming.

Additionally the ceramic matrix composites described herein have one ormore metal carbides homogeneously distributed throughout the matrix. Insome embodiments the metal carbides are distributed on the sub nanometeror molecular level due to the in situ method by which the metal carbidesare formed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A ceramic matrix composite comprising reinforcingfibers and a matrix, wherein the matrix comprises silicon carbide andmetal carbide and the metal carbide is homogeneously dispersedthroughout the silicon carbide.
 2. The ceramic matrix composite of claim1, further comprising a metal boride.
 3. The ceramic matrix composite ofclaim 1, wherein the metal carbides are dispersed on a sub-nanometerlevel.
 4. The ceramic matrix composite of claim 1, wherein the metalcarbides are dispersed on a molecular level.